Spindle device having a dynamic-pressure-fluid bearing

ABSTRACT

In a spindle device mounted to a disc driving apparatus, a mist seal which blocks a mist of lubricating fluid, an oil seal which prevents the lubricating fluid from flowing out, and an oil pool which prevents surplus fluid from flowing out, are combined and disposed so that the lubricating fluid from a dynamic-pressure-fluid bearing is prevented from flowing out or splashing into a clean space. As a result, inconveniences such as a head crush or a head absorption can be avoided, and a reliable spindle device is realized.

This is a divisional application of Ser. No. 09/781,425 filed Feb. 13,2001, now U.S. Pat. No. 6,301,074 which is a divisional of Ser. No.09/151,734, filed Sep. 11, 1998, now U.S. Pat. No. 6,219,199.

FIELD OF THE INVENTION

The present invention relates to a spindle device to be mounted to adisc driving apparatus for driving, e.g., discs, and more particularlyto a structure of a spindle motor of an outer rotor type, which isformed by fixing rotor magnets within a hub that clamps magnetic discs.

BACKGROUND OF THE INVENTION

One of the distinctive trends in computer systems is that memorycapacities are becoming larger and larger due to the extending ofcomputer networks, popularity of engineering work stations, utilizationof data bases and the like. Further, the most common magnetic discdriving apparatus built in computer systems as a memory apparatus hasbeen changed from the 5.25-inch disc drive to the 3.5-inch disc drive,which proves the demand for memory apparatus to be made more compact andslim in size. The demands of magnetic disc driving apparatus, such asthe demands for larger capacity, smaller and slimmer size, naturallylead to demands for a spindle motor (hereinafter called simply a“motor”) mounted to the disc driving apparatus to be of higher accuracyand smaller size. The higher accuracy, among others, is stronglydemanded.

Along with the technology advancement, a memory capacity of the magneticdisc has increased, and the track density of discs can be 8000 TPI(tracks per inch)-10000 TPI, which is converted to a track pitch as fineas 3 μm. The performance required of the motor mounted to the apparatusis to always accurately trace each track having such fine track pitch.This kind of motor has employed ball bearings in general; however, therotation of ball bearings inevitably generates vibration. The level ofvibration is measured to be as fine as ca. 0.15 μm based on NRRO (NonRepeatable Run Out), which is non repeatable sway of the hub of themotor. This vibration level is the minimum possible value for the ballbearings. When this vibration occurs, a magnetic head deviates from atrack by the displacement component due to the vibration. This deviationhas a harmful influence on read/write operation, and the conventionalapparatus employing the ball bearings thus allows almost no margin tomeet the required performance.

Recently, a motor has been proposed in order to improve the accuracy,lower the noise level, and extend the product life. The motor comprisesa fixed shaft, a sleeve that is supported and rotated by the shaft and aradial-dynamic-pressure-fluid bearing, or the motor comprises a fixedsleeve, a rotating shaft that is supported and rotated by the sleeve andthe radial-dynamic-pressure-fluid bearing.

The motor employing the dynamic-pressure-fluid bearing is disclosed inJapanese Patent Application unexamined publication No. H06-178489.

FIG. 16 is a cross sectional view of this conventional motor. In FIG.16, a shaft 501 is vertically fixed at the center of a bracket 504, anda stator core 510 with wires wound thereon is mounted to the bracket504. A rotor magnet 506 is fixed to a rotor frame 505 so that the rotormagnet faces the stator core 510. The rotor frame 505 is mounted to thehub 503. A bushing 511 is fixed at a lower section of an inner rim ofthe hub 503, and another bushing 512 is mounted to an outer rim of thebracket 504. The bushing 511 faces the bushing 512 with a clearancein-between. The magnetic discs (not shown) are to be mounted around thehub 503.

Grooves (not shown) are provided inside of a sleeve 502, the groovesproduce dynamic pressure of lubricating fluid by the rotation of thesleeve 502, which is rotatively supported by the fixed shaft 501 vialubricating fluid. Radial-dynamic-pressure-fluid bearings R501 and R502are thus constructed. Axial dynamic pressure bearings A501 and A502comprise both end faces of a fixed thrust ring 507, a lower face ofrotation thrust ring 508 and an upper face of the sleeve 502. A groove541 is provided on an outer circumference of a cap 509, and anothergroove 542 is provided on an inner circumference of the rotation thrustring 508. The lower rim of groove 541 is disposed at substantially thecenter of groove 542, and the upper rim of groove 542 is disposed atsubstantially the center of groove 541. The upper and lower rims of eachgroove 541 and 542 face each other with some offset.

The conventional motor employing the above dynamic-pressure-fluidbearing has a possible problem that the lubricating fluid might splashinto a space where the magnetic discs are disposed. In this space, amagnetic head reads/writes data from/to the magnetic disc with littleclearance between the head and disc. The space thus must be kept utmostclean because if the lubricating fluid splashes or flows into the space,serious problems such as a head crush, a head absorption, etc. willoccur. (Hereinafter the above space is called the “clean space”.)

The above conventional motor has provided a countermeasure againstlubricating oil splashes by forming an oil pool using the grooves 541and 542 to prevent the lubricating fluid from splashing out from theupper part of the motor; however, this countermeasure cannot prevent amist of lubricating fluid from flowing out.

SUMMARY OF THE INVENTION

The present invention aims to provide a reliable spindle device whichavoids inconvenience such as a head crush or a head absorption bydisposing a mist seal between the thrust-dynamic-pressure-fluid bearingand the clean space where magnetic discs are disposed. The mist sealprevents a mist of lubricating fluid from flowing out into the cleanspace where magnetic discs are disposed.

The spindle device of the present invention comprises the followingelements:

(a) a bracket comprising a fixed shaft and a stator core on which wireis wound,

(b) a hub to which discs are mounted,

(c) a rotor magnet mounted to the hub and facing the stator core,

(d) a sleeve fixed to the hub and rotatively supported by the fixedshaft via the lubricating fluid,

(e) thrust-dynamic-pressure-fluid bearings disposed on both end faces ofthe sleeve, and

(f) a mist seal such as a viscous seal, a labyrinth seal, a magneticfluid seal or the like disposed between thethrust-dynamic-pressure-fluid bearing and the clean space where thediscs are disposed, and the mist seal blocks the mist of lubricatingfluid from flowing out.

The above structure can prevent the mist of lubricating fluid fromsplashing into the clean space by using the mist seal.

Further, an oil seal that prevents the lubricating fluid per se fromflowing out, and an oil pool that prevents surplus lubricating fluidfrom flowing out are combined, whereby liquid lubricating fluid isprevented from flowing out into the clean space. This structure canfurther enhance a reliability of the spindle device.

The spindle device according to the present invention has anadvantageous sealing structure that can prevent the lubricating fluid ofthe dynamic-pressure-fluid bearing from splashing out into the cleanspace. There are the following sealing mechanisms between thedynamic-pressure-lubricating-fluid-bearing and the clean space: oil seal(surface tension seal, centrifugal force seal) and mist seal (viscousseal, magnetic fluid seal, labyrinth seal). Thedynamic-pressure-lubricating-fluid-bearing holds the lubricating fluidusing the surface tension seal, and the centrifugal force seal restoresthe lubricating fluid, further, the mist seal prevents the mist oflubricating fluid from splashing. This sealing process effectivelyprevents the lubricating fluid from flowing and splashing out into theclean space. A part of this arrangement can be omitted depending on themotor construction.

The oil pool and grooves in addition to the above sealing processcontribute to preventing the fluid from flowing as well as splashing outnot only in a continuous operation but also in an intermittentoperation, at rest at a high temperature or with a change inorientation.

The thrust-dynamic-pressure-fluid bearings are disposed on both theupper and lower sections of the radial-dynamic-pressure-fluid bearing,whereby a longer bearing span for the radial-dynamic-pressure-fluidbearing can be obtained, and the rigidity is increased. As a result, thedynamic-pressure-fluid bearing can be well-balanced.

Since the spindle device of the present invention allows no flow-out ofthe lubricating fluid, the bearing is always filled with the lubricatingfluid, which substantially extends a life span of the magnetic discdriving apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a motor used in a first exemplaryembodiment of the present invention.

FIG. 2 is an enlarged view of an upper portion of the motor used in thefirst exemplary embodiment of the present invention.

FIG. 3 is an enlarged view of a lower portion of the motor used in thefirst exemplary embodiment of the present invention.

FIG. 4 details the inside of a sleeve used in the first exemplaryembodiment of the present invention.

FIG. 5 details a thrust-dynamic-pressure-fluid bearing used in the firstexemplary of the present invention.

FIG. 6 is an enlarged view of a lower portion of a motor used in asecond exemplary embodiment of the present invention.

FIG. 7 is a cross section of a motor used in third exemplary embodimentof the present invention.

FIG. 8 is an enlarged view of a lower portion of the motor used in thethird exemplary embodiment of the present invention.

FIG. 9 is a cross section of a motor used in a fourth exemplaryembodiment of the present invention.

FIG. 10 is a cross section of a motor used in a fifth exemplaryembodiment of the present invention.

FIG. 11 is an enlarged view of an upper portion of the motor used in thefifth exemplary embodiment of the present invention.

FIG. 12 is a cross section of a motor used in a sixth exemplaryembodiment of the present invention.

FIG. 13 is an enlarged view of an upper portion of the motor used in thesixth exemplary embodiment of the present invention.

FIG. 14 is a cross section of a motor used in a seventh exemplaryembodiment of the present invention.

FIG. 15 is a cross section of a motor used in an eighth exemplaryembodiment of the present invention.

FIG. 16 is a cross section of a conventional motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are detailed hereinafterby referring to the attached drawings.

(Exemplary Embodiment 1)

FIG. 1 is a cross section of a motor used in a first exemplaryembodiment of the present invention. FIG. 2 is an enlarged view of anupper portion of the motor. FIG. 3 is an enlarged view of a lowerportion of the motor. FIG. 4 details the inside of sleeve used in thefirst exemplary embodiment. FIG. 5 details thethrust-dynamic-pressure-fluid bearing used in the first exemplaryembodiment.

In FIG. 1 through FIG. 5, a shaft 1 is vertically fixed at the center ofa bracket 4 for which screw holes and protruded sections are provided sothat the bracket can be mounted to the disc driving apparatus. A coreholder 12 is also provided in the bracket 4. A stator core 11 of coiledwires is mounted on the outer circumference of the core holder 12 sothat the stator core 11 is situated opposite to a cylindrical rotormagnet 6 via a narrow clearance.

Magnetic discs (not shown) are mounted on an outer circumference of ahub 3. On the inner circumference of the hub 3, the cylindrical rotormagnet 6 is mounted via a cylindrical rotor frame 5. A sleeve 2 ismounted on another circumference of the hub 3. Grooves 17 are providedinside the sleeve 2, the grooves 17 produce dynamic pressure oflubricating fluid (not shown) through rotation of the sleeve 2. Thesleeve 2 is rotatively supported by the fixed shaft 1 via lubricatingfluid, and forms the radial dynamic-fluid-bearings R1 and R2.

On the upper end face of sleeve 2, a rotation thrust ring 8 is fixed,and rotatively supported via the lubricating fluid by a thrust ring 7which is fixed on the fixed shaft 1, thereby forming athrust-dynamic-pressure-fluid bearing A1. The rotation thrust ring 8 hasgrooves 18 which produce dynamic pressure in the lubricating fluid.These grooves 18 can be provided on the fixed thrust ring 7 instead ofon the rotation thrust ring 8. On the lower end face of sleeve 2, arotation thrust ring 10 is fixed, and rotatively supported via thelubricating fluid by a thrust ring 9 which is fixed to an end portion ofbracket 4, thereby forming a thrust-dynamicpressure-fluid bearing A2.The rotation thrust ring 10 has grooves similar to the grooves 18 of onerotation thrust ring 8) which produce dynamic pressure in thelubricating fluid. These grooves can be provided on fixed thrust ring 9instead of on the thrust ring 10.

On the upper side of the rotation thrust ring 8, a seal member 13 isfixed to the sleeve 2 so as to sandwich the ring 8 between the sealmember 13 and the sleeve 2. On the seal member 13, a tapered centrifugalforce seal 16 and an oil pool 30 are provided. The inner circumferenceof hub 3 faces the outer circumference of fixed thrust ring 7 via asmall clearance 15, this small clearance preferably ranging from 0.03 to0.05 mm. On the inner circumference of hub 3, a viscous seal 14 isformed. The viscous seal 14 employs a screw to be rotated for drawingair in from the clean space 29.

An example of the viscous seal has the following structure andmechanism. In a cylindrical space, the screw is provided on an inner orouter circumference that forms the cylindrical space. The screw rotatesto produce pressure so that air flows from the clean space where thediscs are disposed toward the thrust-dynamic-pressure-fluid bearing,whereby the mist of the lubricating fluid is prevented from flowing intothe clean space 29.

On the lower circumference of sleeve 2, a tapered centrifugal force seal21 is provided. An example of a mechanism of the centrifugal force sealnow will be described. The centrifugal force is proportional to a radiusfrom a rotating center, and based on this principle, when the motor isdriven, the lubricating fluid flows toward the dynamic-pressure-fluidbearing by utilizing the taper. A liquid of the lubricating fluid isthus prevented from flowing out.

For a better effect, the centrifugal force seal 21 is disposed on theouter circumference of the rotative sleeve 2.

The lower outer circumference of sleeve 2 faces the inner circumferenceof core holder 12 via a small clearance 20, this small clearancepreferably ranging from 0.03 to 0.05 mm. Another viscous seal 19 isformed on the lower outer circumference of sleeve 2. The viscous seal 19employs a screw that rotates to draw air in from the clean space 29through the space where the senator core 11 and rotor magnet 6 aredisposed.

The above structure allows the centrifugal force seals 16 and 21 toprevent liquid lubricating fluid from flowing out, and allows theviscous seals 14 and 19 to prevent lubricating fluid mist from flowingout into the clean space.

A small annular space is provided between the outer circumference of thering 10 and the inner circumference of core holder 12, whereby a surfacetension seal 24 is formed to provide an oil seal. Further, an oil pool22 is disposed on the core holder 12. These arrangements reinforce theprevention of the flowing out of the lubricating fluid.

The lubricating fluid is filled into the radial-dynamic-pressure-fluidbearings R1 and R2 as well as the thrust-dynamic-pressure-fluid bearingsA1 and A2 when the spindle device is assembled. When the motor isrotated, the lubricating fluid concentrates on the centers of R1, R2, A1and A2. However, surplus fluid does not have a constant flow, andsometimes splashes due to the centrifugal force. When the spindle deviceis assembled, bubbles are incidentally entrapped in the lubricatingfluid. The bubbles grow due to temperature changes, or concentrate andgrow in a lower pressure section in the bearings due to the rotation.The growth of the bubbles pushes up the fluid to cause splashing. Whenthe spindle device is left at a high temperature atmosphere for a longperiod, the lubricating fluid is more likely to leak. In these cases,the spindle device of the present invention can prevent the fluid fromflowing and splashing out into the clean space 29 thanks to acombination of the mist seal, oil seal and oil pool.

(Exemplary Embodiment 2)

FIG. 6 is an enlarged view of a lower portion of a motor used in thesecond exemplary embodiment of the present invention. In FIG. 6, grooves(not shown, but similar to the grooves 17 in FIG. 4) are provided insidethe is sleeve 52. These grooves generate dynamic pressure throughrotation. The sleeve 52 is rotatively supported via the lubricatingfluid by the fixed shaft 1, thereby forming theradial-dynamic-pressure-fluid bearing R2. This embodiment differs fromthe first exemplary embodiment only in the following point: a taperedcentrifugal force seal 25 has a larger taper angle than that in thefirst exemplary embodiment. The tapered seal 25 is disposed as an oilseal on the lower outer circumference of the sleeve 52. In the lowerpart of sleeve 52, in particular, the fluid is subject to flowing outdue to gravity. A larger taper angle is thus preferably employed for thecentrifugal force seal 25 to expand the space. This structure furtherassures the prevention of fluid flow-out.

(Exemplary Embodiment 3)

FIG. 7 is a cross section of a motor used in the third exemplaryembodiment of the present invention. FIG. 8 is an enlarged view of alower portion of the motor.

In FIGS. 7 and 8, this embodiment differs from the first and secondexemplary embodiments in the following points: The stator core 11 ofcoiled wires is mounted to a bracket 54, and a mount collar 62 ismounted at the center of an inner circumference of the bracket 54. Theshaft 1 is fixed at the center of the mount collar 62, and a thrust ring60 is fixed at the end face of the mount collar 62. Grooves forgenerating dynamic pressure are provided on either the thrust ring 60 ora rotating ring 10 mounted to the sleeve 52. Thethrust-dynamic-pressure-fluid bearing A2 is formed by the fixed thrustring 60 and the rotation thrust ring 10 via the lubricating fluid. Thisstructure can also prevent the fluid from flowing out as alreadydiscussed in connection with the first and second exemplary embodiments.

(Exemplary Embodiment 4)

FIG. 9 is a cross section of a motor used in the fourth exemplaryembodiment of the present invention.

This embodiment differs from the first exemplary embodiment in thefollowing points: On a bracket 104, an airtight seal 26 is disposed toseal the screw holes and the like provided on the bracket 104. A smallannular space is provided between the inner circumference of hub 3 andthe outer circumference of bracket 104 whereby a labyrinth seal 27 isformed to provide a mist seal .

In general, the labyrinth seal thus comprises a small clearance and anexpansion room, this small clearance preferably ranging from 0.05 to 0.1mm. Namely, a room 28, where the rotor core 11 coiled by wires and therotor magnet 6 are disposed, is the expansion room, and the annularspace between the hub 3 and the bracket 104 is the small clearance. Airflow energy is consumed in the expansion room 28, and the air flow ratethrough the small clearance decreases substantially, which prohibits themist of lubricating fluid from splashing into the clean space 29.

(Exemplary Embodiment 5)

FIG. 10 is a cross section of a motor used in the fifth exemplaryembodiment of the present invention. FIG. 11 is an enlarged view of anupper portion of the motor.

In FIGS. 10 and 11, a mount collar 212 is mounted to the inner center ofa bracket 204. A shaft 301 is vertically fixed at the center of themount collar 212. On the bracket 204, protrusion sections and screwholes are provided to mount the spindle device to the disc drivingapparatus. On the outer circumference of bracket 204, a stator core 211of coiled wires is mounted to face a rotor magnet 206 via a narrowclearance.

Magnetic discs (not shown) are to be mounted on the outer circumferenceof a hub 203. The cylindrical rotor magnet 206 is mounted to the innercircumference of hub 203 via a cylindrical rotor frame 205. On the innercircumference of hub 203, a magnetic shield panel 210 is mounted forpreventing leakage of magnetic flux. A sleeve 202 is mounted to anotherinner circumference of hub 203. Grooves (not shown, but similar togrooves 17 in FIG. 4) are provided inside the sleeve 202 for generatingdynamic pressure in lubricating fluid through rotation. The sleeve 202is rotatively supported by the fixed shaft 301 via the lubricatingfluid, and thereby forms radial-dynamic-pressure-fluid bearings R201 andR202.

On the upper end of the fixed shaft 301, a thrust ring 207 is mounted toa top screw 201 to be fixed so that the ring 207 can be kept coaxialwith the shaft 301. The fixed thrust ring 207 employs grooves on bothsides for generating dynamic pressure in the lubricating fluid. A thrustbearing A202 is formed and rotatively supported between the sleeve 202and a lower face of the fixed thrust ring 207 via the lubricating fluid.A rotation thrust ring 208 is mounted to the sleeve 202 above the thrustring 207. A thrust-dynamic-pressure-fluid bearing A201 is formed androtatively supported between the upper face of thrust ring 207 and thelower face of thrust ring 208 via the lubricating fluid.

The outer circumference of top screw 201 faces the inner circumferenceof a member 209 for forming a viscous seal 213 via a small annular space214. The viscous seal 213 is provided above the rotation thrust ring208. A screw or helical groove is provided inside the member 209, andthereby forms the viscous seal 213. The screw or helical groove rotatesto draw air in from the clean space 29 so that the viscous seal 213 canprevent the mist of the lubricating fluid from flowing into the cleanspace.

A small annular space 219 is formed between the sleeve 202 and the fixedthrust ring 207, and is filled with the lubricating fluid, which is heldby surface tension. Further a small annular space 220 is formed betweenthe outer circumference of top screw 201 and the inner circumference ofrotation thrust ring 208. The small space 220 is filled with thelubricating fluid, which is held by surface tension.

This surface tension prevents the lubricating fluid from flowing out,and further prevents the mist thereof from splashing above the rotationthrust ring 208. The outer circumference of top screw 201 can be that offixed shaft 301.

An oil pool 217 is disposed between the thrust ring 208 and the member209 so that surplus fluid on the inner circumference of the ring 208travels on the surface of the ring 208 to the oil pool 217 due tocentrifugal force. A groove 218 facing the oil pool 217 is provided onthe top screw 201. If centrifugal force pushes the surplus fluid on theinner circumference of the ring 208 to flow out, the groove 218 canprevent the flow from traveling to the clean space 29. When the motor iskept upside down, the surplus fluid travels along the top screw 201 andreaches the head thereof. If the motor is driven in this attitude, thefluid will splash into the clean space; however, the groove 218 canblock the surplus fluid from travelling down to the head.

A tapered centrifugal force seal 225 is disposed on the lower outercircumference of sleeve 202. For better effect, the seal 225 is disposedon the outer circumference of the rotating body, i.e., sleeve 202, toprevent the lubricating fluid from flowing out. An oil pool 221 isdisposed between the sleeve 202 and the magnetic shield plate 210, andanother oil pool 226 is disposed between the rotor frame 205 and themagnetic shield panel 210. Surplus fluid in the lower part of sleeve 202flows out to the outer circumference of sleeve 202; however, the flow isblocked by the centrifugal force seal 225. If the surplus fluid stilltravels on the outer circumference of sleeve 202 to flow out, the oilpool 221 can block the flow-out from the lower part of sleeve 202. Andyet, if the surplus fluid travels on the magnetic shield panel 210 dueto centrifugal force accompanied by rotation, the oil pool 226 can blockthe flow from flowing out to the clean space 29. A narrow clearance canbe provided to the oil pools 221 and 226 so that the lubricating fluidcan be held by surface tension even if the motor is repeatedly startedand stopped.

The oil pools 221 and 226 are, in addition to other seals, preventivemeasures against draining the fluid into the clean space 29, and theseoil pools further prevent the lubricating fluid from flowing out.

(Exemplary Embodiment 6)

FIG. 12 is a cross section of a motor used in the sixth exemplaryembodiment of the present invention. FIG. 13 is an enlarged view of anupper portion of the motor. In FIGS. 12 and 13, this embodiment differsfrom the fifth exemplary embodiment in the following points: Above therotation thrust ring 208, a magnetic fluid seal holder 309 is fixed tothe sleeve 202. A magnetic fluid seal 314 is fixed to the holder 309,and the seal 314 holds magnetic fluid 313 with magnetic force.

The magnetic fluid seal 314 comprises the following elements:

(a) a ring-shape magnet 315 having N and S poles on respective ends;

(b) ring-shape magnetic members 316 and 317 sandwiching the ring-shapemagnet 315; and

(c) magnetic fluid 313.

The magnetic fluid seal 314 is formed by being encircled with theseelements.

The magnetic fluid 313, as shown in FIG. 13, completely clogs a smallclearance between the outer circumference of the top screw 201 and anend face of the magnetic member 316 opposite to the outer circumference.In this case, the following magnetic path is formed. Magnetic fluxproduced by the magnet 315 travels through the magnetic member 316,magnetic fluid 313 and top screw 201, and arrives at the magnet 315again via a small clearance between the outer circumference of the topscrew 201 and an end face of the magnetic member 317 opposite to theouter circumference. This magnetic path can hold the magnetic fluid 313,whereby the mist of the lubricating fluid is prevented from splashingout from the inner rim of ring 208 into the clean space 29.

Because a room 318 formed by the seal 314 is substantially airtight, themagnetic fluid 313 could possibly be blown out due to a temperaturechange or a pressure difference. This possible blow-out can be avoidedby the following measures: (a) decreasing the capacity of the airtightroom 318, and (b) providing a small annular clearance 220 between thering 208 and the top screw 201 to obtain surface tension which can holdthe lubricating fluid. The height of the lubricating fluid surface thuschanges, which balances pressures, whereby the blow-out is avoided. Thecapacity of the airtight room 318 is preferably less than a capacityenclosed by the inner circumference of the rotation thrust ring and theouter circumference of the top screw. The top screw can be incorporatedinto the fixed shaft.

(Exemplary Embodiment 7)

FIG. 14 is a cross section of a motor used in the seventh exemplaryembodiment of the present invention. In FIG. 14, on a bracket 304, anairtight seal 222 is disposed to seal the screw holes and the likeprovided in the bracket 304. A small annular space is provided betweenthe inner circumference of hub 203 and the outer circumference ofbracket 304 whereby a labyrinth seal 223 is formed to provide a mistseal. In the same manner as the fourth exemplary embodiment shows, anexpansion room 224, where a stator core 211 and a rotor magnet 206 aredisposed, consumes air flow, and the air flow rate through the labyrinthseal decreases substantially, which prevents the mist of lubricatingfluid from splashing into the clean space 29.

(Exemplary Embodiment 8)

FIG. 15 is a cross section of a motor used in the eighth exemplaryembodiment of the present invention. In FIG. 15, this embodiment differsfrom the seventh exemplary embodiment in the following point: A magneticfluid seal 314 is provided, which reinforces the preventive measuresagainst the splash-out of the mist fluid from above the motor.

According to the present invention, combinations of mist seals, oilseals and oil pools can prevent the lubricating fluid from flowing outinto the clean space, whereby a reliable spindle device can be realized.The mist seal prevents a mist of the lubricating fluid from splashingout, the oil seal prohibits the lubricating fluid per se from flowingout, and the oil pool is a measure to prevent surplus lubricating fluidfrom flowing out.

The spindle device of the present invention can be used not only in themagnetic disc driving apparatus, but also other disc driving apparatusesfor optical discs, CD-ROMs, MDs, DVDs and others. Further, the spindledevice also can be used in other apparatuses, and therefore, the spindledevice has a great advantage in industrial applications.

Although illustrated and described herein with reference to certainspecific embodiments, the present invention is not limited to thedetails shown. Rather, various modifications may be made in the detailswithin the scope and range of equivalents of the claims and withoutdeparting from the spirit of the invention.

What is claimed is:
 1. A spindle device comprising: a shaft having afirst end and a second end; a stator; a rotor rotatably supported bysaid shaft via lubricating fluid so as to form aradial-dynamic-pressure-fluid bearing: a magnet opposed to a coiled wirefor causing rotation of said stator relative to said rotor; and amist-proof seal means to create a mist-proof seal adjacent said firstend of said shaft and adjacent said second end of said shaft forpreventing a mist of the lubricating fluid from flowing beyond saidfirst end of said shaft and said second end of said shaft, respectively.2. The spindle device according to claim 1, and further comprising abracket, wherein said shaft and said stator are fixed to said bracket.3. The spindle device according to claim 2, wherein said rotor comprisesa sleeve rotatably supported by said shaft via the lubricating fluid soas to form the radial-dynamic-pressure-fluid bearing, and a hub fixed tosaid sleeve, with said hub being adapted to receive discs thereon in adisc space, and wherein said means to create the mist-proof seal is tocreate the mist-proof seal for preventing mist of the lubricating fluidfrom flowing beyond at least one of said first end of said shaft intothe disc space and said second end of said shaft in to the disc space.4. The spindle device according to claim 3, wherein said stator includesa core having said coiled wire thereon, and said magnet is secured tosaid hub.
 5. The spindle device according to claim 4, wherein saidsleeve has a first end face and a second end face, and furthercomprising a fist thrust-dynamic-pressure-fluid bearing disposed at saidfirst end face and a second thrust-dynamic-pressure-fluid bearingdisposed at said second end face, and wherein said means to create themist-proof seal is disposed between said firstthrust-dynamic-pressure-fluid bearing and the disc space and betweensaid second thrust-dynamic-pressure-fluid bearing and the disc space. 6.The spindle device according to claim 5, wherein said means to createthe mist-proof seal is to create the mist-proof seal by creating aviscous seal.
 7. The spindle device according to claim 5, and furthercomprising an oil-proof seal means to create an oil proof seal at leastone of adjacent said first thrust-dynamic-pressure-fluid bearing andadjacent said second thrust-dynamic-pressure-fluid bearing forpreventing a liquid of the lubricating fluid from flowing beyond saidfirst end of said shaft and said second end of said shaft, respectively.8. The spindle device according to claim 7, and further comprising ahub, with said hub being adapted to receive discs thereon in a discspace, and wherein said means to create the oil-proof seal is to createthe oil-proof seal for preventing liquid of the lubricating fluid fromflowing beyond at least one of said first end of said shaft into thedisc space and said second end of said shaft into the disc space.
 9. Thespindle device according to claim 8, wherein said means to create theoil-proof seal is to create the oil-proof seal by creating a centrifugalforce seal.
 10. The spindle device according to claim 8, wherein saidmeans to create the mist-proof seal is to create the mist-proof seal bycreating a viscous seal, and said means to create the oil-proof seal isto create the oil-proof seal by creating a centrifugal force seal. 11.The spindle device according to claim 5, and further comprising a meansto create a centrifugal force seal disposed on an outer circumferentialsurface of said sleeve.
 12. The spindle device according to claim 5, andfurther comprising a labyrinth seal including a small clearance betweenan inner circumference of said rotor and an outer circumference of saidstator.
 13. The spindle device according to claim 5, and furthercomprising a mount collar fixed to said bracket and coaxiallysurrounding said second end face of said sleeve.